Vaporization cooled transformers



Jan. 8, 1957 c. WHITMAN 2,777,009

VAPORIZATION COOLED TRANSFORMERS Filed Feb. 19, 1953 L. f E E J L non-condensable gas Inventor: Lawrence Qwhibman,

by His Attorney.

United States Patent C VAPORIZATION COOLED TRANSFORMERS Lawrence C. Whitman, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application February 19, 1953, Serial No. 337,802

4 Claims. (Cl. 17415) This invention relates to stationary electrical induction apparatus, and more particularly, to an improved cooling system therefor.

In some conventional forms of stationary electrical induction apparatus the apparatus is submerged within a dielectric liquid within a tank. Above the dielectric liquid, which fills about three quarters of the tank, is an inert gas. During operation of the apparatus heat is produced. This heat is conventionally removed in several ways.

Some of the heat is dissipated from the electrical Windings and magnetic core to the enclosing tank by the phenomena of radiation. The remainder of the heat is carried by conduction through the liquid, and convection currents in the liquid, to the enclosing tank. Only the portions of the tank wetted by the dielectric liquid are acting in these latter processes. The heat is finally dissipated from the tank surface by means of conduction, convection, and radiation to the air surrounding the tank. These processes are well known and generally used.

In these conventional forms of stationary electrical induction apparatus and cooling means therefor, the amount of heat removed by vaporization of the dielectric liquid and condensation of same is relatively small. This seems to be due to the fact that the vapors become intermixed with the non-condensable inert gas in the top portion of the tank. Also, a dielectric liquid conductive to vaporization and condensation cooling possibly is not being used.

I have discovered that if the non-condensable gas and the vapors of the dielectric liquid are prohibited from intermixing, that is, if they are segregated, the amount of heat that can be removed by condensation of the vapors can be increased. Also, if a dielectric liquid is used, which has a boiling point equal to the operating temperature of the electrical windings and core, a greater amount of heat can be dissipated by vaporization and condensation cooling. As the liquid boils, it changes from a liquid state to a vapor state and carries off a large amount of heat. This vapor will pass up through the liquid in the form of bubbles into any open space above the liquid. If this vapor comes into contact with a surface whose temperature is below the boiling point temperature, it will condense on that surface and give up its heat to such surface. This is a desirable way of cooling apparatus since the latent heat of vaporization of most liquids is comparatively high and adds markedly to the heat that can be dissipated by the conventional means.

Consequently, it is an object of this invention to provide an improved cooling system for stationary electrical induction apparatus utilizing vaporization and condensation cooling wherein the vapors of the dielectric liquid and non-condensable gas are segregated.

In a stationary electrical induction apparatus submerged within a vaporizable dielectric liquid within a tank and an inert non-condensable gas above the liquid, my invention consists of an improved cooling system for said apparatus wherein the vapors of said dielectric liquid "ice and the inert gas are segregated, said system comprising a non-condensable gas container open at the top thereof and whose bottom is submerged in said dielectric liquid, the dielectric liquid filling about half of said tank, and the adjacent surfaces of said container and tank being closely spaced to form a narrow duct, said container having a drain pipe extending from the bottom thereof to adjacent the bottom of said tank, the vapors of said dielectric liquid rising in said cooling duct and condensing therein, and forcing said gas up said cooling duct into the container through the top thereof.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawing, in which there is shown a stationary electrical induction apparatus and my improved cooling system therefor.

In the drawing, the stationary electrical induction apparatus is a transformer comprising a magnetic core 1 and electrical windings 2. The transformer is submerged within a vaporizable dielectric liquid 3 which fills about one half of the main tank 4. Bushings 5 are insulatingly mounted in the side walls of the tank or encasing means 4 and are positioned below the surface level 6 of the dielectric and cooling medium 3. Electrical leads extend from the electrical windings 2 to the bush ings 5 which provide terminals for the transformer apparatus. Where the electrical leads are crowded, if desired, the apparatus terminals can be located on the top of the tank 4 or on the tank side walls above the surface level 6 of the cooling liquid.

Within the upper portion of the main tank or encasing means 4 above the surface level 6 of the cooling liquid 3 is an inert non-condensable gas. By a noncondensable gas I mean a gas that will not condense Within the operating temperature and pressure ranges of the apparatus. For instance, a nitrogen or sulphur hexafiuoride gas can be used. Means are provided for segregating this gas and the vapors of the dielectric and cooling liquid 3 formed when the transformer apparatus heats up during operation. This segregating means comprises a non-condensable gas tank or container 7 which is open at the top thereof. There is a cover 8 supported at the top of container 7 in non-closed spaced relationship by appropriate brackets to provide a circumferential opening 9. The cover 8 has a raised ring-like opening 10 in the center thereof. The container 7 is supported near the bottom thereof within the main tank 4 by appropriate brackets and the top of tank 4 is closed by a dome-shaped cover 11. The side walls of the two tanks 4, 7 are closely spaced from each other to form a vapor and condensation duct 12. A drain pipe 13 protrudes from the bottom of the container 7, which is submerged in the liquid 3, to adjacent the bottom of the encasing tank 4. My invention will operate if the liquid level 6 is slightly below the bottom of container 7, however, I prefer that the liquid level 6 be even with or slightly above the bottom of container 7.

During operation of the transformer apparatus some of the heat produced will be carried by the dielectric cooling liquid 3 to the side walls of the main tank 4 where heat will be given up to the ambient air surrounding the main tank 4 by the usual conventional methods. Simultaneously, some of the liquid 3, since it becomes heated up, evaporates. The vapors of the dielectric liquid 3 will rise upwardly in the duct or channel 12. This front of rising vapors Within the duct or channel 12 will sweep or force the gas within the duct 12 ahead O t u the duqt zrand o h t i r I hmu the top thereof via openings 9 and 10. Most of the evaporated cooling liquid. will condense back into a liquid-state while. in the-condensing or cooling duct, 12

and will run back down the duct 12. into- ;the body of thez-dielectric,.liquid 3 Where it can pick up-v more heat.

-Some. of the vapors rising in ,the, duct 12 .may notcondenser therein but -will-. pass with I the non-condensable gas into the container 7. The vapors entering the con- .tainer 7 will ,also-eventually-condense and settle to the bottom thereof. The drain pipe 13 will then conduct these condensedvapors, now intheliquid state, back into the bodyof dielectricv liquid 3.

The drain pipe 13; extends to-adjacent the bottom of the tank 4- so thatvnone of-theyapor bubblesformed will-pass through drain 13 into container 7 but will rise towards thesurface level -6and;are forced to sweep into and'up therestricted duct-12. That is, the vapor bubbles will seektheirescape by-.rising adjacent to the bottom of ontainer 7, andthen will gush; around the periphery of the. bottom of container 7 into the restricted duct 12. Thus, thebottom of;container 7 and the sidewalls of the two tanks 4, 7 constitute abaffle or barrier to direct a rich concentrated stream ofvapor bubbles tothe heat ,dissipatingor condensation surfaces.

;;;Some of the vapors that do not condense within cooling ductl2 will be carried to the area of the domeshaped cover 11. These vapors-will come into contact with the cool cover 11 and condenser This condensa- ;:,tion will, have a tendency to follow the curvature of dome-shaped cover 11 and run downthe main tank side walls for additional cooling, instead of falling directly onto container cover 8. The condensation that does fall onto-cover 8 will of course run off said cover 8 into the-duct 12 and thence back into liquid 3. The raised opening 10 on container cover 8 prevents the condensation failing onto cover 8 fromrunning intocontainer '7, .-.but the non-condensable gas within thetop-dome-shaped :.;-chamber of tank 4 can still pass into .container 7 via -opening 10.

The width of the duct-12 must be of a properdimen- --sion to; realize the ultimate-improvement of segregating .'.;the gas and vapors.- This dimension will-varyas, betweenh-different .size transformers and will .vary also -,-wit;hin the. same sized transformers. However, by way of; example, in the conventional 1-0-kva, pole type transformer, a width of about one quarter of-oneinch has given good results. With such a narrow .duct the front of vapors rising onsweeping up theduct is able to. sweep ..;.the non-condensable gas up -the duct without intermixing ..-,;th e rewith. Thus, the sidewalls of the transforrriertank are swept'by a stream of concentrated vapor-which can condense on the cool transformer side walls unimpeded byathe. non-condensable gas.

Another factor that mustbe considered in realizing ,the a'dvantages of my invention is to. select a dielectric ;.;and-,co oling liquid that has a boiling point within the a desiredpperating temperature range of the-transformer. ThHI is; the dielectric must -be one which-. will,forrn ;vapors.,before the electrical windings become overheated so that a -large quantity of heat is alwaysbeing removed why. vaporization and condensation -cooling.- For in- .--.stance, Freons or fluorocarbons could be used which are characterizedby-boiling point temperatures equal to or slightly below the desired. operating temperature of l the electrical windings in sometransformer installations. This, temperature should be one which will give-normal electricakwinding insulation life. Thus, the boilingpoint ternperature:selected will also depend on the type of insulation selected as -well as considerations of economics ,due; to balance between the more etiicient heat dissipation from the; transformer'tank to the outside air for highentemperatures, and the ,higher losses within transformer apparatus due to increasedwindingresistance as temperatures are increased.

My. .impr y dvcooling sy t m h s, many. advantages. For instance, by using my invention with conventional 10 kva. pole type transformer core and winding parts, approximately a 150% load can be carried without exceeding the normal electrical winding rise, which for a typically designed conventional 10 kva. transformer is about 45 C. Thus, a' 15 .kva. transformer is realized on-10- kva. transformer parts. Because .myimproved cooling system is capable of removing a greater quantity of heat, conventional transformers. equipped. with my cooling system can be safely overloaded without; danger of. overheating ;the apparatus.

Another advantage of my invention is that the weight of conventional transformers can;be reduced. Due to the fact that my cooling system requires that the main tank be filled only about one-half instead of about three-quarters with dielectric fluid, apparatus using my invention will bernuchlighter; For instance, the conventional 15 kvalupole type transformer has a weight ofwabout, 320

pounds. With my invention, a. transformer with-l0 kva.

-parts:will carry a load of 15-- kva.;and will weigh only aboutZOOpounds. Also, because a greater load can now be carried, there is a .saving in space.

That is, a smaller transformer-twill. do=-the job that-heretofore-required a larger transformer.

still-another advantage of mydmproved coolingxrneans is that the operating pressures within transformer tanks usingvaporizationcooling. Because of this, in stationary electrical induction apparatus using my. improved vaporization cooling meansthe tanks do not have to be as strong structurally as with tanks not having my improvement.

' A-iurtheradvantage of my vaporization and condensation-cooling system is that a liquid medium is used as a dielectrio for' the windingsm In some known :forms of vaporization cooling, the vapor alone surrounds the electrical-windings as the dielectric medium. Vapor usually has a smaller dielectric strength than liquids Thislowering of the dielectric-strength is particularly noticeable and objectionablebefore the vapor pressure is fully developed 'underloading and such--vaporization cooled systems required auxiliaryheating before starting or-use of additional higher dielectric strength gases mixed with the vapor.'- My invention does not require these-complications.

My system also operates Without the use of pumps or othermoving auxiliary apparatus which some systems of 1. In an electrical apparatus submerged in a dielectric liquid Within a closed main tank and a non-condensable gas above said liquid, said liquid having a boiling point temperature within the normal operating temperature range of said apparatus, means for segregating said gas and vapors of said liquid formed during operation of'said apparatus, comprising a gas tank open at the top thereof by a peripherally extending opening in an upper portion thereof, said gas tank positioned Within said main'tank with the bottom of said gas tank contacting said liquid, a drain pipe extending from said bottom to-adjacent-the bottom of said main tank,,the side Walls of saidtwo tanks .spaced from each other by approximately one-quarter of one inch to form a narrow condensation and segregating duct, the vapors of said liquid continuously rising in said duct during operation of said apparatus and condensing therein while simultaneously sweeping said non-condensable gas up said duct into said gas tank.

2. In an electrical apparatus submerged in a dielectric liquid within a main tank, said liquid boiling at .a temperature within the normal operating temperature range of said apparatus, a non-condensable gas located above said liquid and means for segregating said gas and the vapor bubbles of said liquid formed during operation of said apparatus, said means comprising a gas container having a raised cover located within the upper portion of said tank, the surface level of said liquid being adjacent the bottom of said container, and the side walls of said tank and container closely spaced with respect [to each other to form a narrow segregating and condensation duct, the vapor bubbles rising in said duct in a concentrated front and sweeping said gas into said container adjacent the top thereof, and said vapor bubbles condensing in said duct, said tank having a dome-shaped cover spaced from said raised cover, the vapor bubbles rising to between said dome-shaped cover and raised cover condensing on said dome-shaped :cover and running along the curvature of said dome-shaped cover onto the cool side walls of said tank.

3. In a stationary electrical induction apparatus submerged within a dielectric liquid within a main tank having a non-condensable gas above said liquid, an improved vaporization cooling system for said apparatus comprising an open non-condensable gas container for said gas positioned within said main tank, the side walls of said tank and container being closely spaced from each other to form a condensation duct, the surface level of said liquid being positioned adjacent to the bottom of said container and said liquid having a boiling point temperature within the normal operating temperature range of said apparatus, said container having a raised cover with a raised ring-like opening therein, said raised cover and the uppermost peripheral edge of said open container defining a peripheral opening, the vapor bubbles formed in said liquid during operation of said apparatus rising in said duct and condensing therein and sweeping said noncondensable gas into said gas container through said two container openings, the main tank being closed and having a dome-shaped cover thereon, the vapor bubbles reaching said dome-shaped cover condensing thereon and flowing along the curvature of said dome-shaped cover onto the side walls of said tank, any condensation falling onto the raised cover of said container being prohibited from passing into said container through said raised opening but flowing freely off said raised cover into said duct.

4. In an electrical apparatus which is submerged within .a dielectric liquid within a closed tank, only the approximately lower half of said tank having said liquid therein and a non-condensable gas located in said tank above said liquid, said liquid having :a boiling point temperature within the normal operating temperature range of said apparatus, means for segregating the vapors :of said liquid from said non condcnsable gas comprising a container positioned within the other half of said tank, the walls of said container being closely spaced with respect to the side Walls of said tank and defining *a narrow duct therebetween, the upper end of said container being open, the bottom of said container being disposed within and slightly below .the surface of said liquid, :and a drain extending from said bottom to adjacent the bottom of said tank.

References Cited in the file of this patent UNITED STATES PATENTS 5 13,42l Rowland Jan. 23, 41894 1,93 l,373 Clark Oct. 17, 1933 1,953,216 'Elsey Apr. 3, 1934- 2,447,883 Whitman Aug. 24, 1948 

